import java.util.Scanner;

/**
 * 饮料换购
 */
public class BuyDrinks {
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        //在此输入您的代码...
        int n = scan.nextInt();
        int sum = n;
        while (n >= 3) {
            n -= 3;
            n += 1;
            sum += 1;
        }
        System.out.print(sum);
        scan.close();
    }
}
